An existing Long Term Evolution (LTE) system includes two types of frame structures. A frame structure type 1 is shown in FIG. 1: One radio frame includes 20 timeslots whose lengths are 0.5 ms, and one subframe includes two adjacent timeslots. The frame structure is applied to frequency division duplex (FDD). A frame structure type 2 is shown in FIG. 2: One radio frame includes two half radio frames whose lengths are 5 ms, and each half radio frame includes five subframes whose lengths are 1 ms. In the five subframes, there are four normal subframes and one special subframe. The normal subframe includes two timeslots whose lengths are 0.5 ms. The special subframe includes three special timeslots: a downlink pilot timeslot (DwPTS), a guard period (GP), and an uplink pilot timeslot (UpPTS). The frame structure is applied to time division duplex (TDD). For TDD, seven uplink-downlink configurations shown in Table 1 exist in the existing system.
TABLE 1Downlink-to-uplinkswitch-pointperiodicity(Downlink-Uplink-to-UplinkdownlinkSwitch-config-pointSubframe numberurationperiodicity)012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
In the LTE system, to support a hybrid automatic repeat request mechanism, user equipment needs to feed back a hybrid automatic repeat request-acknowledgment (HARQ-ACK) of physical downlink shared channel (PDSCH) transmission to a base station by using a physical uplink control channel (PUCCH) and a physical uplink shared channel (PUSCH). The hybrid automatic repeat request-acknowledgment may also be referred to as an ACK (acknowledgment)/NACK (negative acknowledgment) for short. The user equipment needs to receive, by using a physical hybrid automatic repeat request indicator channel (PHICH), an HARQ-ACK corresponding to a physical uplink shared channel (PUSCH).
In the LTE system, for FDD, an HARQ-ACK corresponding to a PDSCH transmitted in a downlink subframe n−4 is fed back in an uplink subframe n; for TDD, an HARQ-ACK corresponding to a PDSCH transmitted in a downlink subframe n-k is fed back in an uplink subframe n, and k belongs to a set K. A definition of K for each TDD uplink-downlink configuration is shown in Table 2.
TABLE 2Uplink-downlinkSubframe nconfiguration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, 6————8, 7,——4, 63——7, 6, 116, 55, 4—————4——12, 8, 7, 116, 5, 4, 7——————5——13, 12, 9, 8, 7,———————5, 4, 11, 66——775——77—
It can be learned from Table 2 that in an existing TDD system, different uplink-downlink configurations have different HARQ-ACK timing, and complexity of the TDD system is higher than that of an FDD system.